Effect of GSM-900 RFR on HSP expression in brain immune cells
Résumé
Objective. We have previously demonstrated that some radiofrequency signals are not able to induce HSP expression in both neuronal (SH-SY5Y) and astrocytic (U87) cell lines (BEMS 2003, Maui, USA). We have added to these data by focusing on another brain cell type: the microglial cells that constitute the brain immune system. Methods. The human microglial cell line (CHME5) was used as a model. These cells were cultured in DMEM medium supplemented with stable glutamine, 10 % FCS and 1% antibiotics. Cell density was 1.2. 106 per 35 mm petri dish. In vitro exposure to GSM-900 microwaves was performed using a wire-patch antenna at 2 W/kg during 1 hr (n=4). Shamexposed samples were run in the same way in a non-activated wire-patch antenna placed in a second identical incubator. Immediately and 4 hr after exposure, cells were fixed in PBSparaformaldehyde (4%) for immunocytochemistry. Anti-Hsp27, anti-Hsc70 and anti-Hsp70 antibodies were used. The first antibody was revealed using an FITC-labeled antibody. The level of heat shock protein expression was estimated using image analysis (Aphelion software). Positive controls for heat shock protein induction were performed by exposing the cells to a heat shock at 43 or 45 C for 1 hr or 20 min respectively and for recovery period of 4, 6 and 24 hr (n=3). Results. The Hsc70 form is constitutively expressed in the CHME5 line and its expression is significantly induced 4 hr after a twenty min exposure at 45 C. However, exposure to GSM-900 RFR at 2 W/kg during 1 hr did not increase the expression of Hsc70 even 4 hr after the exposure. Exposure to radiofrequency signals did not induce expression of Hsp70, 1 or 4 hr after exposure. Following a 43 C exposure we noticed an increase in Hsp70 expression only after 24 h of recovery. We therefore cannot exclude the possibility that radiofrequency signals could induce the expression of Hsp70, 24 hr after exposure, and this will need further investigations. Finally, we were not able to induce Hsp27 expression under any heat shock conditions tested, which means either that the cell line does not express the 27 kDa form or that the chosen heat shock treatments are not efficient to induce Hsp27. Discussion and Conclusion. Our results suggest that radiofrequency signals are not able to induce HSP expression in the microglial cell line CHME5. These results are in agreement with our previous observations in neuronal and astrocytic cells, although some exposure conditions need to be added. Our data differ from those obtained by others groups using non-brain cells. This discrepancy may be caused by different sensitivity of cells to radiofrequency signals